Project Summary ?-Synuclein phosphorylated at Serine 129 is a marker of pathologic fibrillar aggregates in hallmark Lewy body inclusions in Parkinson's disease (PD) and Dementia with Lewy Bodies, but the precise reason for this post- translational modification and its role in the pathogenesis of these disorders remain unclear. This project aims to address this knowledge gap by studying the role that protein phosphatase 2A (PP2A) mediated dephosphorylation of ?-synuclein plays in the molecular etiology of these disorders. PP2A is a member of a family of conserved enzymes that constitute the majority of serine/threonine phosphatase activity in the brain and function as master regulators of cellular phosphoregulatory networks, controlling key processes required for protein homeostasis and cell survival. PP2A is a trimeric enzyme composed of a catalytic C subunit, a scaffolding A subunit, and a regulatory B subunit each of which is encoded by multiple genes and multiple splice isoforms. The substrate specificity of PP2A is determined by its subunit composition, which is regulated by methylation of its catalytic C subunit, and this methylation is controlled by both a dedicated methylesterase, PME-1, and a dedicated methyltransferase, LCMT-1. The PP2A isoform responsible for dephosphorylating ?-synuclein is methylation dependent, and pharmacological inhibition of PME-1-dependent PP2A demethylation mitigates the phenotype of ?-synuclein transgenic mice. To study the role of PP2A and its methylation in ?-synucleinopathies, we will alter PP2A activity in vivo by manipulating PME-1 and LCMT-1 expression using genetically modified mice. Specific aim 1 will test the hypothesis that reducing PP2A methylation, via increased PME-1 expression, exacerbates ?-synucleinopathies by increasing the pathogenicity of ?-synuclein. Aim 2 will test the hypothesis that enhancing PP2A methylation, via increased LCMT-1 expression, protects against ?-synucleinopathies by reducing the pathogenicity of ?-synuclein. And aim 3 will determine if manipulating PP2A methylation impacts ?-synuclein mediated pathology through phosphorylation at Serine 129. By the completion of these studies we will gain greater insight into the pathogenetic role of PP2A in ?-synucleinopathies and advance it as a potential disease modifying therapeutic target for these disorders.